Non-Hermitian topology in a multi-terminal quantum Hall device

Quantum devices characterized by non-Hermitian topology are predicted to show highly robust and potentially useful properties for precision sensing and signal amplification.

However, realizing them has remained a daunting experimental task, as non-Hermiticity is often associated with gain and loss, which would require precise tailoring to produce the signatures of nontrivial topology. Based on the insight that reflection matrices describing waves reflected from the boundaries of topological insulators exhibit non-Hermitian topological signatures, we propose ways to realize non-Hermitian topology in the conductance matrix of topological multiterminal devices. Here, instead of gain and loss, we use the nonreciprocity of quantum Hall edge states to directly observe non-Hermitian topology in the conductance matrix of a multi-terminal quantum Hall ring. Our simulations and transport measurements evidence a robust, non-Hermitian skin effect, characterized by currents and voltages showing an exponential profile that persists across Hall plateau transitions away from the regime of maximum non-reciprocity. Our observation of non-Hermitian topology in a quantum device introduces a scalable experimental approach to construct and investigate generic non-Hermitian systems.